An integrated circuit generally comprises multiple logic components such as logic gates, interconnected to form logic paths for performing various operations, such as calculation, etc. A logic path especially connects an input to an output and crosses a number of logic gates.
Some of these logic paths may potentially be considered as critical paths, especially when the times of propagation through these paths are the highest. Such critical paths determine the circuit performance and especially set the extreme conditions for the circuit to operate properly. For example, the logic path for which the propagation or processing time is the highest sets the maximum operating frequency of the circuit. Further, a path can be considered as critical when it is particularly sensitive to the value of the power supply voltage for the proper operation of the circuit portion relative thereto, or when it is particularly sensitive to a temperature variation or to an abrupt voltage variation.
It is thus important to be able to determine the critical paths from among the logic paths of the circuit. Different tools enabling to determine such critical paths exist and are thus not detailed hereafter.
It is further also important to be able to monitor the logic paths considered as critical, to predict a possible failure of the circuit in specific operating conditions. To achieve this, it is known to implement a replica of each of the paths to be monitored. This replica path especially is a sub-optimal reproduction of the path to be monitored. More specifically, this replica path is a circuit which especially applies the same logic function to an input signal as the path to be monitored, but differs from the path to be monitored in a few parameters such as, for example, the propagation delay or the threshold voltage, so that the failure of the replica path occurs before that of the path to be monitored. Another solution comprises introducing, at the end of the critical path, a detection flip-flop anticipating the arrival of the signal on the output flip-flop. This intrusive solution, called “canary detection”, increases the delay of the critical path, and is thus banned.